Fluid-type shale retorting



June 23, 1953 L. A. NICOLAI- 2,643,218

FLUID-TYPE SHALE' RETORTING Fild June 16, 1949 2 Sheets-Sheet 2 Patented June 23, 1953 FLUID-TYPE SHALE RETORTING Lloyd A. Nicolai, Baton Rouge, La., assignor to 7 Standard Oil Development Company, a corporation of Delaware Application June 16, 1949, Serial No. 99,456

6 Claims. (Cl. 202-44) The present invention relates to the art of retorting or distilling oil-bearing minerals, such as oil shale, oil sands, tar sands, and the like, maintained in the form of subdivided particles in a highly turbulent state, fluidized by upwardly flowing gases to resemble a boiling liquid, wherein the heat required for distillation is supplied by burning spent solid distillation residue in a separate combustion zone and circulating hot solid combustion residue to the distillation zone. More particularly, the present invention relates to improved means for preventing losses of product by excessive combustion thereof in the combustion zone and for reducing solids entrainment in the gases and vapors leaving the fluid bed in the distillation retort.

The invention will be fully described hereinafter with reference to the accompanying drawing wherein Figure 1 is a graphical summary of experimental data demonstrating the utility of the invention, and

Figure 2 is a schematical illustration of a sys- 'tem suitable for carrying out a. preferred embodiment of the invention.

Prior to the present invention it has been proposed to carry out the distillation of oil shale in the form of subdivided solids varying in particle size from a fine powder up to rather large aggregates of, say, about inch diameter in a highly turbulent fluidized state while supplying the heat required by this reaction as sensible heat of hot solid combustion residue in the manner indicated above. It has been observed in this type of operation that substantial product losses are caused by an excessive build up of carbon in the distillation zone and the subsequent combustion of said carbon in the combustion zone. Another problem arises as the result of a strong tendency of the shale to disintegrate rapidly in the course of the pyrolytic treatment to particles having an extremely small size of about -20 microns which is the unit particle size of the shale silt. For example, Colorado shale, when subjected to a fluid-type distillation, quickly forms a mass containing about 70% of fines of 0-20 microns size, and this even if the shale is charged in rather coarse aggregates. At the conditions of fluid shale distillation, these fines are fully entrained by the fiuidizing gases and rapidly carried overhead from the fluidized beds in the distillation and combustion zones, causing losses of carbonaceous constituents, complicating liquid product recovery due to slurry formation and detrimentally affecting the fluidity of the fluidized beds.

It has now been found that th carbon concentration in the retort is strongly influenced by the chemical composition of the burned shale and that this composition and with it the carbon concentration in the retort may be changed by a suitable treatment with a gas reacting with at least one constituent of the burned shale. EX- perimental data indicate that a substantial portion of the carbon of the spent shale fines in the retort has been picked up in the retort'by spent low-carbon shale fines returned to the retort from the combustion zone. These low-carbon fines have a high adsorption and/or polymerization activity causing the adsorption of oil vapors evolved in the retort and the formation of a carbon deposit on these fines, which results in corresponding product losses and in a substantial increase of their gas buoyancy and entrainment rate. It is this adsorption and/or polymerization activity and with it product adsorption and carbon concentration of the fines in the retort, which have been found to be strongly afiected by the chemical composition of the burned shale fines and by gas treatments aiiecting this chemical composition. More particularly, it has been found that the adsorption and/or polymerization activity of the burned shale fines may be substantially reduced by a treatment of the burned shale fines with a reducing gas, particularly hydrogen, which chemically reacts with at least one constituent of said fines at conditions suitable for such reaction, prior to the return of the burned shale fines to the fluidized bed in the retort. Similar effects may be obtained by treating of the burned shale with CH4 or other reducing gases. The present invention in its broader aspect resides in treating the burned shale fines in this manner.

Specific treating conditions depend on the gas used as well as on the temperature to which the fines to be treated have been subjected in the combustion zone. However, in general treating times of about 1 to 10 minutes at substantially the temperature of combustion which may be about 900-l200 F2, are adequate for the purposes of the invention.

The effect of treatments in accordance with the invention is substantiated by the experiments reported below.

Example I Spent retorted shale having a particle size through mesh was burned in a batch fluidized bed at a temperature of about 1000 F. to an organic carbon content of about 0.06 wt. About 10 parts by weight of the burned shale were fluidized at 1000 F. with N2 for about 15 minutes. Thereafter, one part by weight of a raw shale ground to -20 mesh and having a Fischer assay of about 26 gals. of oil per ton was added and the mixture was further fluidized at about 1000 F. for 1.5 minutes. Thereafter the mixture was separated into 10 parts less than 100 mesh and 1 part greater than 100 mesh, and the through 100 mesh fraction was analyzed for organic carbon. The entire test was repeated three times. It was found that organic carbon of the through 100 mesh burned shale had increased on the average by about 0.20 wt. at the end of the test.

Example II Burned shale obtained as in Example I was fluidized with H2 at 1000 F. for about 60 minutes. Thereafter H2 was replaced by N2 as the fluidizing gas and'coarse fresh'shale was added'at the conditions of Example I. This test wa repeated three times. Organic carbon on the burned shale had increased by-only about 0.07 wt. on the average.

Example I'II Burned shale obtained as in Examples I and II was fluidized with N2 at 1000 F. Thereafter N2 was replaced by methane for'about seconds and then fresh shale was added while fluidizing with methane. This test was repeated three times. The average increase in organic carbon on burned shale was found to be only 0.14 wt.

Example IV Burned shale'obtained as in the'previousexamples was fluidized with N2 at 1100 F. llhere after N2 was replaced-by H2 for one minute at the same temperature. N2 was reintroduced to displace the H2 whereupon the fluid bed was cooled to 1000 F. and fresh shale added as described in Examples I-III. The test was repeated three times. The average increase in organic carbon on the burned shale amounted to 0.10.

Example V Burned shale obtained as above was fluidized and heated to 900 F. in a mixture of H2 'and N2 in equal proportions. Total heating time was about 15 minutes. Thereafter raw shale was added as above. The test was repeated three times. The average increase inorganic carbon on the burned shale was found to be 0.13 wt.

The data reported above demonstrate that a suitable treatment with a reactive gas of the type specified and particularly with H2, substan tially reduced the adsorbed-carbonconcentration on the burned fines in the retort whilean essentially inert gas such as N2 has no such effect. The effect of the treatment of the present invention is, therefore, basically different from that of conventional substantially physical stripping treatments.

While it is not intended to tie the present invention to any theory of the reaction mechanism involved or to limit the scope of the invention by any such theory, it is believed that the adsorption activity of the burned shale results from its loss of carbonate carbon as CO2 and an increase of its oxidation potential in the course of the combustion reaction whereby the'burned shale is activated and that the centers of activation so created are saturatedand thus deactivated and the oxidation potential is reduced by the treatment with reactive gasesin accordance with the invention. For example, treatment with H2 and other reducing gases may remove occluded or other reactive O2 and hydrate or otherwise saturate centers of activation. The carbonate carbon theory is substantiated by ample experimental evidence which is summarized in Figure 1. In the graph shown, weight percent of carbon adsorbed per pass through the retort is plotted against weight percent of carbonate carbon in the burned shale. The curve which is based on experimental data obtained in fluid-type twovessel shale retorting shows a definite relationship supporting at least in part the theory advanced above.

The present invention has utility in all conventional fluid-type two-vessel shale retorting systems wherein the shale is retorted in one or more fluid-type vessels and heat for retorting is supplied as sensible heat of hot spent shale burned in'a separate heater and returned to the fluidized shale in the retorting zone substantially at the burner temperature. A typical system of this type is schematically illustrated in Figure 2 of the drawing and will be hereinafter briefly described with reference to a preferred-embodiment of the present invention.

Referring now to Figure 2, the system illustrated therein essentially comprises a distillation vessel or retort H), a stripper or second stage retort 30, a combustion chamber or burner 40, and a burned shale modifying zone or treater'fifl, the functions and cooperation of which will be forthwith described using as an examplethe retorting of a Colorado oil shale having a Fischerassay of about 26 gals. of oil per ton of shale.

In operation, fresh shale crushed to aiparti'cle size of about 4-30*mesh is supplied'throughline -l to retort 10 at a rate controlled by valve 3. Simultaneously, a gas such as product tail gas, steam, CO2 or other inert gas containing suspended therein hot solids supplied from burner 40, as will appear more'clearlyhereinafter, is fed to the lower .portion of retort "[0 from line 12 through a suitable distributing device, such 'as grid [4. Retort IO-is so designed that'atthetprevailing conditions .of solidsclrculation and :carrier gas :rates the superficial linear velocity of the gasiform medium in retort I0 is about 0.5-1.5 ft. per sec. Suflicient hot solids from burner 40 are supplied with the gas throughiline l2 and grid I4 at an adequate temperature'to maintainwithin retort I 0 a solids temperature of about 900-1200 F., for example about 950 suitable for shale distillation. At'the conditions specified a fluidized highly turbulent relatively dense shale bed M10 having a well'defined upper interface L10 is formed in retort I0 and distillation takes place therein. As a result, the fresh shale disintegrates' rapidly to form about50 70% of fines having aparticle'size of 0-201microns.

At equilibrium conditions, bed-'Mio may have a particle size distribution about as follows:

Particle Size Weight 0-10 microns I5-35 10 20 microns 20-30 20- 80 micronS 5-15 '80 microns-35 mesh 10-20 On 3.5 mesh Us-. 15-25 The average carbon concentration in the retort is maintained substantially below0.7 weight sayat about 0.2 to' 0.4 weight by thecombined action of'carbon removal in burner'40"andburned m shale treatment in accordance with the invena result, the fines entrainment rate from retort i is relatively low, say about 0.002 to 0.004 lb. per cu. ft. of overhead gases and vapors and bed M10 may be readily maintained in a relatively dense fluidized state. Simultaneously, the product transfer rate from the retort to the burner is maintained at a desirable minimum.

l he mixture of product vapors and gases with fluidizing gas passing overhead from level L10 together with entrained solids enters a gas-solids separation system such as one or more cyclones i wherein most of the entrained solids may be separated and returned to bed M through one or more dip-pipes l8. Vapors and gases now containing merely about 0.0001 to 0.0004 lb. per cu. ft. ofentrained solids fines are passed through line it to a conventional product recovery system (not shown). Such concentration of solids lines in the product vapors may be readily removed by scrubbing and filtering without causing appreciable difliculties by slurry formation. if desired, solids so removed may be returned to retort ill in the form of an oil slurry.

A mixture of freshly retorted and burned spent shale particles is withdrawn from retort [0 through line 22 and may be passed into a fluidtype stripper 50. A stripping gas, such as steam or 092, is supplied to the bottom of stripper through line it and grid 26 at a rate adequate to establish in stripper 30 a turbulent fluidized mass Mao having an upper interface L30 similar to mass M10 in retort iii. Stripper 30 may be operated at conditions similar to those maintained in retort it. Such operation serves the dual purpose of removing adhering product vapors from the shale flowing from retort l0 and of completing the retorting process. In other words, stripper 55 may represent a second shale retorting stage whereby the total holding time of the shale charged may be substantially reduced at any given temperature as compared with single stage operation. Stripper overhead passes through line 28 into retort it, to be mixed therein with the overhead from bed M10.

Shale, now substantially denuded of distillable constituents and containin an average of about 0.2 to 0.4 weight percent of organic carbon and about 3.5 to 5.5 weight percent of carbonate carbon, is passed from stripper 30 through line 32 into line 35 wherein it is picked up by a combustion-supporting gas, such as air, which may be preheated to about 600-800 F. in heat exchange with process flue gases. The amount of air supplied to line 35 is preferably sufficient for a substantially complete combustion of the organic carbon on the solids carried by line 35. About 0.0025 to 0.0035 mol of oxygen per lb. of fresh shale charged are usually sufficient for this purpose. The suspension formed in line 35 is passed through a distributing grid 31 or the like to the lower portion of burner which is so designed that the gases flow upwardly therein at a superficial linear velocity of about 1-3 ft. per second, so a to form a relatively dense fluidized bed M40 having a well defined upper interface L40.

The temperature in bed M40 is preferably maintained about -200 F. higher than that of bed M10, say at about 1050 F. For this purpose bed M40 may be cooled by any suitable cooling means such as cooling coil 42 in heat exchange with water or steam. Steam so generated and/or superheated may be used in the process. If desired, heat may be'withdrawn by continuously circulating burner solids through extraneous cooling means and back to bed M40 in a manner known per se. A dilute suspension of spent shale fines in flue gases is passed overhead from interface L40 through a gas-solids separation system 44 comprising one or more cyclones and/or electrical precipitators from which separated solids may be returned to bed M40 through line 46 or discarded through line 48. Flue gases substantially free of entrained solids may be vented through line 50, if desired after suitable heat recovery. Additional burner solids may be discarded through line 52 from bed M40, if desired for a proper maintenance of the solids balance in the system.

Solid combustion residue substantially free of organic carbon is withdrawn from the bot-tom of bed M40 via line 55 at a rate controlled by valve 51. The solids flowing through line 55 enter the top of treater 00 which may have the form of a pipe section of larger diameter than pipe 55 so as to provide for a relatively extended solids holding time in treater B0 of about 1 to 5 minutes at the rate of solids flow through line 55. A reducing gas, such as H2 preferably preheated at least to the temperature of bed M40 of about 1000- 1100 F., is supplied through one or more gas lines 02 to the bottom of treater 50 to flow upwardly therethrough countercurrently to the burned hot shale. Excess treating gas and gaseous reaction products may be either passed upwardly through line 55 into burner 40 or withdrawn from the system through line 63. In the former case an additional desirable stripping of oxygen and flue gas is accomplished. The treated shale leaves treater 60 through line 64 substantially at the temperature of burner 40 and at a rate controlled by valve 06. The latter valve may assist in adjusting the bed level and thus the holding time in treater 00.

The solids flowing through line 64 enter line l2, are suspended therein in fluidizing gas and supplied to retort ID as described above, substantially at the temperature of bed M40. These solids may have an organic carbon content of about 0.0 to 0.1 weight percent and a carbonate carbon content of about 4 to 5 weight percent when Hz was used as the treating gas in treater 30 at about 1050" F. Their adsorption activity is substantially reduced as a result of the gas treatment in accordance with the present invention.

The solids circulation rate through line l2, Which is approximately the same as that through line 35, depends on the exact temperature diflerential between burner 40 or treater 60 and retort it. At the conditions specified above it may be about 10 to 15 lbs., say about 12 lbs., per lb. of fresh shale fed through line I. Treatment of the burned shale in accordance with the present invention reduces the carbon pick-up by the burned shale in the retort at least by 50%. The significance of thi improvement may be fully appreciated from the fact that a carbon pick-up of as little as 0.1 weight percent on the burned shale per pass corresponds to a product loss of as much as about 13% of the distillable content of the fresh shale charged.

Various modification of the system described with reference to the drawing may appear to those skilled in the art without deviating from the spirit of the invention.

The above description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

1. In the process of distilling oil-bearing minerals of the type of oil shale which disintegrate during: distillation; wherein thersubdivided. min erals are subjected to: a distillation temperature in the form: of: a: highly turbulent dense mass fluidized by an upwardly flowing gasiform medium in= a-distillation zone and the heat required by thedistillation is supplied by burning solid distillationresidue with a combustion-supporting gas the form ofafluidizedma'sso'f s'olid's in a separate-combustionzone-at a combustion tem perature an'd returning solid combustion residue substantially at said combustion temp'eraifure' to said distillation zone, the improvement which comprises subjecting said combustion residue, prior tO itS return to saiddistillation zone; to a chemical reaction witha red'ucing'gas by passing said combustion residue" downwardly through a separate treatingzone countercurrently to an upflowing reducing gas'reac'ting' chemically with at least oneconstituent of said; combustion residue, and contacting said combustionresidue with said reducing gas in said" treatlng'zone' at temperatures" of about 900'1 200" F. and contact timesof about l-l'flminute's adequate to'pro'mote said chemical reaction.

2'. The process ofcl'aim 1 in which said re'act'- 25 mg gas is'hydrogen.

3 The: process oi claim 1 inwhich said reacting gas is CHr.

4. The process of claim 1- in which said reaction temperature is not substantially lower than said-combustion temperature.

5; Theprocessofclaim l inwhich the organic carbon content of said mass in said distillation zone is maintained" substantially below about 0.7 weight percent.

6; 'I-he'process of claim- 1 in which the carbonate: carbon content of said' distillation residue is not substantially reduced duringsaid combusti'onv LLOYD A; NICOLAI.

References Cited in theme of this patent UNITED" STATES PATENTS Number Name Date 2 444935 Corson-et al June 29, 1948 2,480,670 Peck Aug. 30, 1949 OTHER REFERENCES Bureau of" Mines Information Circular I. C. 7348, pages'50, 51. 

1. IN THE PROCESS OF DISTILLING OIL-BEARING MINERALS OF THE TYPE OF OIL SHALE WHICH DISINTEGRATE DURING DISTILLATION, WHEREIN THE SUBDIVIDED MINERALS ARE SUBJECTED TO A DISTILLATION TEMPERATURE IN THE FORM OF A HIGHLY TURBULENT DENSE MASS FLUIDIZED BY AN UPWARDLY FLOWING GASIFORM MEDIUM IN A DISTILLATION ZONE AND THE HEAT REQUIRED BY THE DISTILLATION IS SUPPLIED BY BURNING SOLID DISTILLATION RESIDUE WITH A COMBUSTION-SUPPORTING GAS IN THE FORM OF A FLUIDIZED MASS OF SOLIDS IN A SEPARATE COMBUSTION ZONE AT A COMBUSTION TEMPERATURE AND RETURNING SOLID COMBUSTION RESIDUE SUBSTANTIALLY AT SAID COMBUSTION TEMPERATURE TO SAID DISTILLATION ZONE, THE IMPROVEMENT WHICH COMPRISES SUBJECTING SAID COMBUSTION RESIDUE, PRIOR TO ITS RETURN TO SAID DISTILLATION ZONE, TO A CHEMICAL REACTION WITH A REDUCING GAS BY PASSING SAID COMBUSTION RESIDUE DOWNWARDLY THROUGH A SEPARATE TREATING ZONE COUNTERCURRENTLY TO AN UPFLOWING REDUCING GAS REACTING CHEMICALLY WITH AT LEAST ONE CONSTITUENT SAID COMBUSTION RESIDUE WITH DUE, AND CONTACTING SAID COMBUSTION RESIDUE WITH SAID REDUCING GAS IN SAID TREATING ZONE AT TEMPERATURE OF ABOUT 900*-1200* F. AND CONTACT TIMES OF ABOUT 1-10 MINUTES ADEQUATE TO PROMOTE SAID CHEMICAL REACTION. 